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Inhibition of aged microplastics and leachates on methane production from anaerobic digestion of sludge and identification of key components
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Researchers investigated the effects of aged microplastics and their leachates on sludge anaerobic digestion, finding that aged PVC and PET significantly inhibited methane production, with phthalate esters and bisphenol A identified as key inhibitory components.
Large amounts of microplastics (MPs) accumulate in the sludge anaerobic digestion system after being treated by the wastewater treatment plants, inevitably leading to aging and chemicals leaching. However, no information is available about the effects of aged MPs and leachates on the anaerobic digestion of sludge. In this study, the effects of different aged MPs ((polyethylene (PE), polyethylene terephthalate (PET), polyvinyl chloride (PVC), and polylactic acid (PLA)) and leachates on anaerobic methanogenesis of sludge were investigated. PLA-related treatments caused no adverse effects on anaerobic digestion. While PE-, PET-, and PVC-related treatments significantly inhibited methane production with an order of leachates (26.4-42.4 %) > MPs (16.1-22.9 %) > aged MPs (2.4-11.8 %). For different leachates, PET leachate caused the strongest inhibitory effects. The same order was found for the methane potential and hydrolysis coefficient. These results suggest that the inhibition of MPs on methanogenesis is mainly caused by the leachates. Based on biochemical and microbial community analysis, the primary mechanism is that the leachates induce oxidative stress, damaging microbial cells and reducing microbial activity, consequently inhibiting methanogenesis. Furthermore, via effect-directed analysis, methyl benzoate (MB), dimethyl phthalate (DMP), and 2,4-Di-tert-butylphenol (DTBP) were identified as key components in the PET-leachate inhibiting anaerobic methanogenesis.
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PVC microplastics were added to anaerobic sludge digestion systems at concentrations of 10–60 particles/g, finding that low concentrations (10 particles/g) slightly increased methane production (+5.9%) while higher concentrations inhibited it by up to 24.2%, with inhibition linked to bisphenol-A leaching from PVC. The study reveals a non-linear dose-dependent effect of PVC microplastics on biogas production in wastewater treatment.
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Researchers used plasma treatment to precisely control polypropylene microplastic aging and tested its effects on anaerobic sludge digestion, finding that while unaged microplastics strongly inhibited methane production, optimally aged microplastics at a carbonyl index of 0.219 recovered methane yield to 83%.
Revealing the Mechanisms of Polyethylene Microplastics Affecting Anaerobic Digestion of Waste Activated Sludge
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Researchers studied how polyethylene microplastics affect the anaerobic digestion of sewage sludge, a common wastewater treatment process. They found that higher concentrations of microplastics significantly reduced methane production by disrupting microbial communities and enzyme activities essential for digestion. The study reveals that microplastic contamination in wastewater systems can undermine the efficiency of sludge treatment and biogas generation.
Revealing How Polyvinyl Chloride Microplastic Physicochemically Affect the Anaerobic Digestion of Waste Activated Sludge
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